Direct-current traction power supply system and method for connecting photovoltaic power generation system to urban rail transit

Abstract

The invention discloses a direct-current traction power supply system and method for accessing a photovoltaic power generation system into urban rail transit, and the system comprises an in-station direct-current bus wiring point and a line direct-current traction network wiring point which form an input point of rail transit traction power supply; the photovoltaic power generation system is electrically connected with an input point of the rail transit traction power supply so as to supply power; the photovoltaic power generation system comprises a grid-connected device, a converter and a photovoltaic array, the photovoltaic array is electrically connected with the converter so that voltage transmitted by the photovoltaic array can be converted and boosted through the converter, the converter is electrically connected with the grid-connected device, and the grid-connected device is provided with a direct-current output bus. And the direct current output bus is electrically connected with a direct current bus wiring point in the station, or the direct current bus is electrically connected with a line direct current traction network wiring point, so that electric energy generated by the photovoltaic array is converted and then is directly input to the direct current bus wiring point in the station or the line direct current traction network wiring point. The technical problems of high centralized grid connection loss and low power generation efficiency of traditional station photovoltaic power generation are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of rail transit power supply, and more specifically, relates to a photovoltaic power generation system connected to a direct current traction power supply system of urban rail transit and a method thereof. Background Art

[0002] Photovoltaic power generation technology is relatively mature and is constantly innovating and developing. In the field of rail transit, photovoltaic power stations are built in ground locations such as depots, parking lots, and ground stations to provide clean, low-carbon energy for rail transit systems. At present, urban rail transit photovoltaic power generation systems mainly adopt the technical solution of AC busbar grid connection. After convergence, it is converted into AC power through a DC-AC inverter and then connected to a low-voltage AC400V busbar for power and lighting. Its technical characteristics are that the grid connection points are relatively concentrated, which is suitable for photovoltaic power generation systems with concentrated photovoltaic arrays and close to substations.

[0003] With the development of photovoltaic building integration and photovoltaic sound barrier integration technology, the distribution of photovoltaic power generation components in urban rail transit shows a trend from centralized distribution to linear development. The traditional station centralized grid-connected solution will lead to high cable investment and large line losses in the later operation. Moreover, after the photovoltaic installed capacity increases, it will exceed the absorption capacity of power and lighting loads, and photovoltaic power generation cannot be fully utilized.

[0004] Therefore, technical personnel in this field urgently need to invent a rail transit DC traction power supply system that can significantly reduce grid-connected cable investment, reduce photovoltaic grid-connected losses, improve the comprehensive power generation efficiency of photovoltaic power generation systems, and stabilize traction grid voltage to solve the above-mentioned technical problems. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, in order to reduce the investment in grid-connected cables, reduce photovoltaic grid-connected losses, improve the comprehensive power generation efficiency of photovoltaic power generation systems, and stabilize the traction network voltage, in a first aspect, the present invention provides a photovoltaic power generation system connected to a DC traction power supply system for urban rail transit, including: a DC bus connection point in a station, a line DC traction network connection point, and a photovoltaic power generation system; The DC bus connection point in the station and the DC traction network connection point of the line are the input points of the rail transit traction power supply; The photovoltaic power generation system is electrically connected to the input point of the rail transit traction power supply to provide power; wherein, the photovoltaic power generation system includes a grid-connected device, a converter and a photovoltaic array, the photovoltaic array is electrically connected to the converter, so that the voltage transmitted by the photovoltaic array is converted and boosted through the converter, the converter is electrically connected to the grid-connected device, and the grid-connected device has a DC output bus; the DC output bus is electrically connected to the DC bus wiring point in the station, or the DC bus is electrically connected to the DC traction network wiring point of the line, so that the electric energy generated by the photovoltaic array is directly input to the DC bus wiring point in the station or the DC traction network wiring point of the line after conversion.

[0006] In the first aspect, the system includes several urban rail transit stations, and two adjacent urban rail transit stations are connected through a line DC traction network, and several line DC traction network connection points are formed on the line DC traction network; and each of the urban rail transit stations is provided with an in-station DC bus connection point.

[0007] In the first aspect, the photovoltaic array is composed of a plurality of photovoltaic power generation groups arranged in parallel, and each of the photovoltaic power generation groups is electrically connected to a grid-connected device via a corresponding converter.

[0008] In a second aspect, the present invention provides a power supply system for urban rail transit, comprising: The photovoltaic power generation system is connected to the DC traction power supply system of urban rail transit; A city power grid, wherein the city power grid has a power output terminal for outputting alternating current; A transformer and rectifier assembly, electrically connected to the power output terminal, for converting the alternating current into direct current; Among them, the city power grid transforms the city-end power through the transformation and rectification components and inputs it into the photovoltaic power generation system to connect to the urban rail transit DC traction power supply system for power supply of the urban rail.

[0009] In a second aspect, the transformer and rectifier assembly includes a main transformer, a step-down transformer and a traction transformer electrically connected in sequence.

[0010] In the second aspect, it also includes a controller, and a monitoring device, a signal transmission device and an alarm device electrically connected to the controller. The monitoring device includes a circuit monitoring device for monitoring the voltage value input from the urban power grid to the urban rail, and inputting the voltage value data into the controller. The controller is used to determine whether the voltage value is within a preset voltage range based on the input voltage value data. If it is determined that the voltage value is not within the preset voltage range, a fault signal is sent through the signal transmission device, and at the same time, the alarm device is controlled to sound an alarm.

[0011] In the second aspect, the warning device includes a buzzer or a signal light.

[0012] In a third aspect, the present invention provides a method for connecting a photovoltaic power generation system to a DC traction power supply system of urban rail transit, comprising: S1, constructing a photovoltaic array consisting of multiple parallel photovoltaic power generation groups to form an initial current; S2, converting and boosting the initial current through a converter to form a boosted current with preset voltage parameters; S3, inputting the boosted current into the grid-connected device to form a pre-used direct current; S4, connecting the pre-used direct current to the current input point of the urban rail transit direct current traction power supply system for power supply.

[0013] In the third aspect, the S4 step comprises: S41, connecting the pre-used DC power to the DC positive and negative busbars in the DC switch cabinet of the substation.

[0014] In the third aspect, the S4 step comprises: S42, connecting the pre-used DC power to the section traction network via a DC cable.

[0015] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art: 1. By building a photovoltaic power generation system connected to the urban rail transit DC traction power supply system, an efficient and comprehensive photovoltaic grid-connected solution is provided for various photovoltaic power generation scenarios such as rail transit stations and sections. Specifically, the photovoltaic power generation system is connected to the input point of the rail transit traction power supply consisting of the DC bus connection point in the station and the line DC traction network connection point, thereby solving the technical problem of centralized grid connection of traditional stations in the existing technology.

[0016] 2. Furthermore, the photovoltaic power generation system includes a grid-connected device, a converter and a photovoltaic array. The photovoltaic array is electrically connected to the converter so as to transform and boost the voltage transmitted by the photovoltaic array through the converter. The converter is electrically connected to the grid-connected device, and the grid-connected device has a DC output bus. The DC output bus is electrically connected to the DC bus wiring point in the station, or the DC bus is electrically connected to the DC traction network wiring point of the line, so that the electric energy generated by the photovoltaic array is directly input into the DC bus wiring point in the station or the DC traction network wiring point of the line after conversion, and then the low-voltage DC point formed by the conversion of the photovoltaic array is converted into a DC voltage suitable for use in the rail transit traction power supply system through the converter.

[0017] 3. By constructing a photovoltaic power generation system connected to the urban rail transit DC traction power supply technology, the investment in photovoltaic system grid-connected cables can be significantly reduced, the photovoltaic grid-connected cable losses can be reduced, the utilization efficiency of the photovoltaic power generation system can be improved, and the green and low-carbon development direction of urban rail transit can be met. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the line connection of the photovoltaic power generation system connected to the urban rail transit DC traction power supply system in an embodiment of the present invention; Figure 2 A diagram of a DC traction power supply system for large-capacity photovoltaic access; Figure 3 This is a diagram of a small-capacity photovoltaic access DC traction power supply system; Figure 4 A schematic diagram of the line connection for the photovoltaic power generation system to the DC bus connection point in the station; Figure 5 A schematic diagram of the line connection point of the photovoltaic power generation system access line DC traction network; Figure 6 A flowchart of the method for connecting a photovoltaic power generation system to DC traction in urban rail transit.

[0019] Description of reference numerals: 1. DC bus connection point in the station; 2. DC traction network connection point of the line; 3. Photovoltaic power generation system; 301. Photovoltaic array; 302. Converter; 303. Grid-connected equipment; 4. Urban rail transit station; 5. Urban power grid; 6. Main transformer; 7. Step-down transformer; 8. Traction transformer. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] Embodiment 1: See also Figure 1-6 , the present invention provides a photovoltaic power generation system connected to a DC traction power supply system for urban rail transit, comprising: a DC bus connection point 1 in a station, a line DC traction network connection point 2 and a photovoltaic power generation system 3; The DC bus connection point 1 in the station and the DC traction network connection point 2 of the line are input points of the rail transit traction power supply; the photovoltaic power generation system 3 is electrically connected to the input point of the rail transit traction power supply to provide power; wherein, the photovoltaic power generation system 3 includes a grid-connected device 303, a converter 302 and a photovoltaic array 301, the photovoltaic array 301 is electrically connected to the converter 302, so that the voltage transmitted by the photovoltaic array 301 is converted and boosted through the converter 302, the converter 302 is electrically connected to the grid-connected device 303, and the grid-connected device 303 has a DC output bus; the DC output bus is electrically connected to the DC bus connection point 1 in the station, or the DC bus is electrically connected to the DC traction network connection point 2 of the line, so that the electric energy generated by the photovoltaic array 301 is directly input into the DC bus connection point 1 in the station or the DC traction network connection point 2 of the line after conversion.

[0022] The photovoltaic power generation system of the present invention is connected to the urban rail transit DC traction power supply system, which has significant advantages over the traditional station centralized grid-connected solution. In the traditional solution, the centralized grid connection leads to high cable investment, large line losses in later operation, and with the increase of photovoltaic installed capacity, the absorption capacity of power lighting loads is limited, resulting in photovoltaic power generation cannot be fully utilized. In contrast, the present invention directly connects the photovoltaic power generation system 3 to the DC bus connection point 1 or the line DC traction network connection point 2 in the station, effectively reducing cable investment and operating losses, while improving the utilization rate of photovoltaic power generation.

[0023] As for the location of the DC bus connection point 1 in the station, it is the DC positive and negative bus in the DC switch cabinet inside the rail transit station. For the photovoltaic power generation system 3 located near the station, the rectified standard voltage and current can be directly connected to the positive and negative bus to supply power to the rail transit; as for the line DC traction network connection point 2, it is the DC power supply line located between the rail transit stations, and the rectified standard voltage and current can be directly connected to the DC power supply line for power supply; The photovoltaic power generation system 3 includes a grid-connected device 303, a converter 302 and a photovoltaic array 301. The photovoltaic array 301 is responsible for collecting solar energy and transmitting it to the converter 302. The converter 302 converts and boosts the voltage generated by the photovoltaic array 301, and then directly connects it to the DC bus connection point 1 in the rail transit station or the DC traction network connection point 2 of the line through the DC output bus of the grid-connected device 303. This direct connection method simplifies the power supply process, reduces energy loss in the intermediate links, and improves the energy efficiency of the system. In addition, since the photovoltaic power generation system 3 is directly connected to the DC traction power supply system of the rail transit, it can make full use of photovoltaic power generation, avoiding the problem of the increase in photovoltaic installed capacity exceeding the power lighting load absorption capacity in the traditional solution, and realizing the full absorption of photovoltaic power generation. This design not only improves energy utilization efficiency, but also reduces dependence on traditional energy sources, providing a green and economical power supply solution for urban rail transit. In a preferred implementation manner of this embodiment, the system includes a plurality of urban rail transit stations 4, and two adjacent urban rail transit stations 4 are connected via a line DC traction network, and a plurality of line DC traction network connection points 2 are formed on the line DC traction network; and each of the urban rail transit stations 4 is provided with an in-station DC bus connection point 1.

[0024] In the above embodiment, the system covers multiple urban rail transit stations 4, which are interconnected through a line DC traction network to form a continuous power supply network. The line DC traction network is provided with multiple line DC traction network connection points 2 to facilitate power access and distribution; at the same time, each urban rail transit station 4 is equipped with an in-station DC bus connection point 1, ensuring that the photovoltaic power generation system 3 can directly and efficiently input electrical energy into the DC traction power supply network of the rail transit, thereby realizing power interconnection between stations and optimal energy configuration.

[0025] In a preferred implementation of this embodiment, the photovoltaic array 301 is composed of a plurality of photovoltaic power generation groups in parallel, and each of the photovoltaic power generation groups is electrically connected to a grid-connected device 303 via a corresponding converter 302 .

[0026] For the DC 750V traction power supply system, the configurations of photovoltaic power generation systems 3 with different capacities are as follows: 1. For photovoltaic power generation systems with a capacity of 500kW~600kW, the grid-connected equipment configuration is: 1 DC output circuit breaker with a rated current of 800A, 3 DC input circuit breakers with a rated current of 250A, and 1 set of unidirectional conduction diodes; the number and capacity of converters: 3 200kW DC / DC converters; 2. For photovoltaic power generation systems with a capacity of 600kW~800kW, the grid-connected equipment configuration is: 1 DC output circuit breaker with a rated current of 1000A, 4 DC input circuit breakers with a rated current of 250A, and 1 set of unidirectional conduction diodes; the number and capacity of converters: 4 200kW DC / DC converters; 3. For photovoltaic power generation systems with a capacity of 800kW~1MW, the grid-connected equipment configuration is: 1 DC output circuit breaker with a rated current of 1250A, 5 DC input circuit breakers with a rated current of 250A, 1 set of unidirectional conduction diodes; number and capacity of converters: 5 200kW DC / DC converters; 4. For photovoltaic power generation systems with a capacity of more than 1000kW, two or more grid-connected cabinets are used for grid connection, and the DC / DC converter is configured according to the actual installed capacity.

[0027] Embodiment 2: The present invention provides a power supply system for urban rail transit, including a photovoltaic power generation system connected to a DC traction power supply system for urban rail transit, a city power grid 5 and a transformer and rectifier assembly. The urban power grid 5 has a power output end for outputting alternating current; a transformer and rectifier component is electrically connected to the power output end for converting the alternating current into direct current; wherein, the urban power grid 5 transforms and converts the urban-end power through the transformer and rectifier component and inputs the transformed power into the photovoltaic power generation system to connect to the urban rail transit DC traction power supply system for powering the urban rail.

[0028] Specifically, the system outputs AC power through the power output end of the urban power grid 5, converts it into DC power through the transformer and rectifier components, and directly inputs it into the photovoltaic power generation system to connect to the urban rail transit DC traction power supply system, providing stable power for urban rail transit. Specifically, the power output end of the urban power grid 5 is electrically connected to the transformer and rectifier components, which are responsible for converting AC power into DC power to meet the power supply needs of urban rail transit. This design optimizes the configuration of external power supplies, improves the efficiency of external power supplies, reduces the number of external power supplies by 30% to 50%, reduces the stringent requirements for the site selection of external power supplies, and the distance between the external power supply and the traction station can be extended from 1 to 2 km to 3 to 4 km. At the same time, the system improves the level of energy conservation and carbon reduction, reduces the total power consumption by 10% to 20%, eliminates the on-board brake resistor, helps to lighten the train, and reduces the train operation loss and the environmental control cost of the underground passage. In addition, the system has improved power supply capacity and safety and reliability. The traction network voltage has been increased from 500V~900V to 650V~900V. For external power supply N-2 failure and traction station N-2 failure, the train can be powered uninterruptedly while maintaining the same traffic density. The design of this power supply system not only improves energy utilization efficiency, but also reduces dependence on traditional energy, providing an efficient and economical power solution for urban rail transit.

[0029] In some preferred embodiments, the transformer and rectifier assembly includes a main transformer 6, a step-down transformer 7, and a traction transformer 8 that are electrically connected in sequence. The city power grid 5AC110kV is the starting point of power supply and provides high-voltage alternating current. The main transformer 6 converts the high-voltage alternating current into a lower voltage alternating current AC35kV / AC10kV. The step-down transformer 7 reduces the AC35kV / AC10kV voltage to AC400V and supplies it to the traction transformer 8. The traction transformer 8 receives the AC400V voltage and converts it into a voltage suitable for the traction motor. The rectifier link converts the alternating current output by the traction transformer 8 into direct current DC1500V / DC750V and supplies it to the train.

[0030] In some preferred embodiments, a controller is further included, as well as a monitoring device, a signal transmission device and an alarm device electrically connected to the controller. The monitoring device includes a circuit monitoring device for monitoring the voltage value input from the urban power grid 5 to the urban rail, and inputting the voltage value data into the controller. The controller is used to determine whether the voltage value is within a preset voltage range based on the input voltage value data. If it is determined that the voltage value is not within the preset voltage range, a fault signal is sent through the signal transmission device, and at the same time, the alarm device is controlled to sound an alarm.

[0031] In some preferred embodiments, the alarm device includes a buzzer or a signal light.

[0032] For the above strength, the urban rail transit power supply system of this embodiment significantly improves the reliability and safety of the system by integrating advanced intelligent monitoring and fault response mechanisms. Specifically, the system includes a photovoltaic power generation system connected to the urban rail transit DC traction power supply system, a city power grid 5, and a transformer and rectifier component, which is responsible for converting the AC power of the city power grid 5 into DC power for rail transit use. In addition, the system also includes a controller, a monitoring device, a signal transmission device and an alarm device electrically connected thereto, wherein the monitoring device is responsible for real-time monitoring of the voltage value input to the rail transit by the city power grid 5, and feeding back the data to the controller. The controller determines whether the voltage value is normal according to a preset voltage range. Once an abnormality is detected, a fault signal is sent through a signal transmission device, and an alarm device is activated to sound an alarm, which can be a buzzer or a signal light, to achieve a quick response. This design not only improves the stability of the power supply system, but also enhances the ability to respond to abnormalities in the power supply system through real-time monitoring and instant feedback mechanisms, thereby ensuring the continuous operation of urban rail transit and the safety of passengers.

[0033] Embodiment three: The present invention provides a method for connecting a photovoltaic power generation system to a DC traction system of an urban rail transit, comprising: S1, constructing a photovoltaic array consisting of multiple parallel photovoltaic power generation groups to form an initial current; S2, converting and boosting the initial current through a converter to form a boosted current with preset voltage parameters; S3, inputting the boosted current into the grid-connected device to form a pre-used direct current; S4, connecting the pre-used direct current to the current input point of the urban rail transit direct current traction power supply system for power supply.

[0034] In some preferred embodiments, the S4 step comprises: S41, connecting the pre-used DC power to the DC positive and negative busbars in the DC switch cabinet of the substation.

[0035] In some preferred embodiments, the S4 step comprises: S42, connecting the pre-used DC power to the section traction network via a DC cable.

[0036] For the two optional modes of power transmission by the photovoltaic power generation system in the above embodiment: The first type is that for photovoltaic power stations or photovoltaic building integrated power generation systems near stations, the station DC bus grid-connected solution can be adopted. The station DC bus grid-connected solution consists of the following: 1) Photovoltaic modules are connected in series to form a photovoltaic array.

[0037] 2) The photovoltaic array is connected to the DC / DC converter (capacity 100~200kW) via a dedicated photovoltaic cable, and the photovoltaic power generation voltage is boosted through DC / DC conversion. For the DC1500V traction power supply system, the voltage is boosted to DC750V~900V. For the DC1500V traction power supply system, the voltage is boosted to DC1500V~1800V.

[0038] 3) The DC / DC converter is connected to the DC grid-connected cabinet or DC grid-connected equipment through a DC cable. According to the capacity of the photovoltaic power generation system, the DC grid-connected cabinet is equipped with input and output DC circuit breakers of appropriate capacity. When the capacity is small, the DC grid-connected equipment is used, and the DC grid-connected equipment is only equipped with one input and output.

[0039] 4) The DC grid-connected cabinet is connected to the DC positive and negative busbars in the DC switch cabinet of the substation via a DC cable.

[0040] The second type is to use the line DC bus grid-connected solution for photovoltaic power generation equipment or photovoltaic building integrated power generation systems near the line. The line DC bus grid-connected solution consists of the following: 1) Photovoltaic modules are connected in series to form a photovoltaic array.

[0041] 2) The photovoltaic array is connected to the DC / DC converter (capacity 100~200kW) via a dedicated photovoltaic cable, and the photovoltaic power generation voltage is boosted through DC / DC conversion. For the DC1500V traction power supply system, the voltage is boosted to DC750V~900V. For the DC1500V traction power supply system, the voltage is boosted to DC1500V~1800V.

[0042] 3) The DC / DC converter is connected to the DC grid-connected cabinet via a DC cable. According to the capacity of the photovoltaic power generation system, the DC grid-connected cabinet is equipped with input and output DC circuit breakers of different capacities.

[0043] 4) The DC grid-connected cabinet is connected to the traction network and running rails via DC cables.

[0044] It will be easily understood by those skilled in the art that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. The photovoltaic power generation system is connected to the urban rail transit DC traction power supply system, which is characterized by: include: A DC bus connection point (1) in a station and a DC traction network connection point (2) on a line, wherein the DC bus connection point (1) in a station and the DC traction network connection point (2) on a line are input points for rail transit traction power supply; A photovoltaic power generation system (3), the photovoltaic power generation system (3) being electrically connected to an input point of the rail transit traction power supply to provide power; wherein the photovoltaic power generation system (3) comprises a grid-connected device (303), a converter (302) and a photovoltaic array (301); the photovoltaic array (301) being electrically connected to the converter (302) to convert and boost a voltage transmitted by the photovoltaic array (301) through the converter (302); the converter (302) being electrically connected to the grid-connected device (303); the grid-connected device (303) having a DC output bus; the DC output bus being electrically connected to a DC bus connection point (1) in the station, or the DC bus being electrically connected to a DC traction network connection point (2) of the line, so that the electric energy generated by the photovoltaic array (301) is directly input to the DC bus connection point (1) in the station or the DC traction network connection point (2) of the line after conversion.

2. The photovoltaic power generation system according to claim 1 is connected to the urban rail transit DC traction power supply system, characterized in that: The system comprises a plurality of urban rail transit stations (4), two adjacent urban rail transit stations (4) are connected via a line DC traction network, a plurality of line DC traction network connection points (2) are formed on the line DC traction network; and each of the urban rail transit stations (4) is provided with the station DC bus connection point (1).

3. The photovoltaic power generation system according to claim 1 is connected to the urban rail transit DC traction power supply system, characterized in that: The photovoltaic array (301) is composed of a plurality of photovoltaic power generation groups arranged in parallel, and each photovoltaic power generation group is electrically connected to a grid-connected device (303) via a corresponding converter (302).

4. The power supply system of urban rail transit is characterized by: include: The photovoltaic power generation system according to any one of claims 1 to 3 is connected to a DC traction power supply system for urban rail transit; A city power grid (5), the city power grid (5) having a power output terminal for outputting alternating current; A transformer and rectifier assembly, electrically connected to the power output terminal, for converting the alternating current into direct current; The city power grid (5) transforms the city-end power through the transformer and rectifier components and then inputs it into the photovoltaic power generation system to connect to the city rail transit DC traction power supply system for powering the city rail transit.

5. The power supply system for urban rail transit according to claim 4, characterized in that: The transformer and rectifier assembly comprises a main transformer (6), a step-down transformer (7) and a traction transformer (8) which are electrically connected in sequence.

6. The power supply system for urban rail transit according to claim 4, characterized in that: It also includes a controller, and a monitoring device, a signal transmission device and an alarm device electrically connected to the controller. The monitoring device includes a circuit monitoring device for monitoring the voltage value input from the urban power grid (5) to the urban rail, and inputting the voltage value data into the controller. The controller is used to determine whether the voltage value is within a preset voltage range based on the input voltage value data. If it is determined that the voltage value is not within the preset voltage range, a fault signal is sent through the signal transmission device, and at the same time, the alarm device is controlled to sound an alarm.

7. The power supply system for urban rail transit according to claim 6, characterized in that: The alarm device includes a buzzer or a signal light.

8. A method for connecting a photovoltaic power generation system to a DC traction system of urban rail transit, characterized in that: include: S1, constructing a photovoltaic array consisting of multiple parallel photovoltaic power generation groups to form an initial current; S2, converting and boosting the initial current through a converter to form a boosted current with preset voltage parameters; S3, inputting the boosted current into the grid-connected device to form a pre-used direct current; S4, connecting the pre-used direct current to the current input point of the urban rail transit direct current traction power supply system for power supply.

9. The method for connecting a photovoltaic power generation system to urban rail transit DC traction according to claim 8, characterized in that: The S4 step includes: S41, connecting the pre-used DC power to the DC positive and negative busbars in the DC switch cabinet of the substation.

10. The method for connecting a photovoltaic power generation system to urban rail transit DC traction according to claim 8, characterized in that: The S4 step includes S42, connecting the pre-used DC power to the section traction network via a DC cable.

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